The invention relates to a positive eccentric dobby for driving the heald shafts of a loom having eccentrically disposed cam discs attached to a camshaft, which drives pivoted roller levers on a rigidly mounted roller lever shaft with minimal clearance.
A positive eccentric dobby for looms having a heald shaft coordination device is shown in Swiss Patent Specification CH 260 546. A camshaft used to drive the heald shafts and having associated cam discs can be displaceably or tiltably moved, so that when there is a clearance between the cam discs and rollers, the heald shafts can return to a starting position because their dead weight produces a coordination of the heald shafts; i.e. places all heald shafts in the same position. A single position for the coordination of the heald shafts does not meet the requirements of the various operating sequences of a loom, such as, for example, the cleaning of a weft duct, or various operating states, such as, for example, the disengagement of the warp threads.